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The cause of fish dying in the Duzi River remains “inconclusive”, according to a statement issued following a meeting between Umgeni Water, Msunduzi Municipality and the Duzi Umgeni Conservation Trust.

The meeting was held to discuss the deaths of many fish discovered in the Duzi at Ashburton last week, as well as recent multiple leaks into the river from the Darvill Wastewater Treatment Plant.

Umgeni Water said the spillage into the river are due to multiple power outages suffered by the Darvill plant over the last few weeks.

Umgeni Water spokesperson Shami Harichunder said power supply interruptions between November 21 and November 25 to the Darvill plant caused the storm dam on the Darvill site to spill “large volumes of untreated and highly concentrated sewage into the Msunduzi River on numerous occasions”.

Harichunder said the low river flow volumes coupled with the fact that the sewage wasn’t properly diluted, and high and rapid changes in temperature were thought to have greatly increased the problem at Darvill.

He said an estimated 20 ML (megalitres) of sewage originating from the Pietermaritzburg area — possibly including some industrial effluent — is believed to have entered the Msunduzi River directly before reaching Darvill plant due to infrastructure problems in the collector sewer systems.

Harichunder said Darvill’s biological activated sludge treatment process was also severely affected by power problems. This resulted in some poorly treated effluent also leaking out.

He said the combined events could have contributed to the death of largely carp and scalie fish that were discovered at Ashburton.

He said other species of fish remained unaffected downstream. “Low food availability, temperature stress and lack of fish refuge could have also contributed,” added Harichunder.

He said however that without any definitive information from analysis and sampling it cannot be said conclusively that the death of the fish was the consequence of the events in the second to last week of November or that the fish deaths are linked directly to industrial effluent, “although this cannot be ruled out entirely”.

He said discussions between the municipality and Umgeni Water would be ongoing regarding the possibility of the plant being excluded from load-shedding.

“The municipality has undertaken corrective action on the faults that have caused the problems.”

Harichunder said they would also reduce the impact of pollutants in the Duzi by releasing water from Henley Dam over the next two days.

“Sampling upstream of the Darvill effluent outfall has shown sewage presence for several months prior to the events in late November.

“The effect of sewage losses upstream of Darvill will clearly affect river water quality, especially from the Baynespruit,” he said.

Harichunder said that power supply to Darvill should be considered a high priority.

He said at this stage it is not possible to provide stand-by power generation capacity to run Darvill, but a co-generation project is being planned. “A constructed wetland project is also close to implementation that would take any spills of untreated sewage from the storm dam through additional ponds.”

Meanwhile, responding to questions about the blocked manhole leaking raw sewage into the Duzi at Camps Drift which The Witness also reported on recently, Msunduzi municipal spokesperson Ntobeko Ngcobo said they had tried to unblock it with the equipment they had, however the leak developed again.

“We conducted a further investigation and the work that needs to be done requires a high pressure jetting machine.”

She said they were in the process of hiring a machine as theirs is undergoing repairs.

“We appeal for patience, noting the inconvenience that this has caused to the members of the community,” she said.

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